TECHNICAL SUPPORT
Published 2026-03-10
When debugging theservo, have you ever encountered this situation: The connection is correct and the code does not report an error, but theservojust won't obey the command, either shaking non-stop, or getting stuck halfway through the rotation? Don't worry, this is a pitfall that almost everyone who playsservos will step into. The servo looks simple, but in fact there are many tricks inside it. From selection to power supply to signal interference, a small mistake in any link can make you struggle for a long time. This experimental report will sort out the pitfalls we have encountered and the solutions to help you successfully control the steering gear.
The servo shakes, which is what we often call "shaking" or "swaying back and forth". This is usually caused by unstable signals or voltage fluctuations. Especially when using PWM wave control, if the frequency of the control signal does not match the internal circuit of the servo, it will be "at a loss" and appear to be spinning back and forth. We found in the experiment that the jitter is particularly obvious when using direct power supply, because the 5V output current on the board is limited. Once the servo requires a large current for an instant, the voltage will be pulled down, causing the control chip to reset and the signal will be messed up. The most direct way to solve this problem is to prepare a separate external power supply for the servo, such as several batteries or a voltage stabilizing module, and completely separate the power supplies of the control board and servo.
Wiring looks simple, but it is the hardest hit area for failed experiments. Servos generally have three wires: power wire (usually red), ground wire (brown or black), and signal wire (orange or yellow). Many people ignore the key point that the power line and the ground line must be "shared ground". What does it mean? It is the power supply of your control board (such as a microcontroller) and the servo. Their negative terminals must be connected together. If they are not grounded together, the signal voltage sent by the control board and the reference voltage received by the servo will not be accurate, and the signals will naturally be messed up. ️ The correct connection method is: the power line and ground wire of the servo are connected to the external power supply, and the negative pole (ground) of the external power supply is connected to the ground of the control board. Finally, the signal wire is connected to the IO port of the control board.
When choosing a power supply for the servo, you can't just look at whether the voltage is correct, but whether the current is sufficient is the key. The metal steering gear we used in our experiment has a nominal stall current of one or two amps. If you use a power supply with an output capacity of only 500mA, once the servo rotates with load, the current is insufficient and the voltage drops immediately. At worst, the torque is insufficient and it cannot turn, or at worst, the control board restarts. Therefore, when choosing a power supply, it is best to choose one with stable voltage and current output capability greater than the maximum operating current of the servo. For example, for a single small servo, it is recommended to use a power supply of more than 1A; if it is a high-torque servo or drives multiple ones at the same time, a 2A or even 5A switching power supply is required. Don't think about saving trouble and taking power directly from the 5V pin of the development board.
Sometimes the code and wiring have been checked several times, but the servo just won't move. At this time, don't rush to suspect that the servo is broken. First check whether the signal wire is loose. It is also possible that the PWM initialization and configuration are not done properly. The PWM pins of many microcontrollers do not output waveforms by default. You have to set the frequency and duty cycle in the program first. In terms of frequency, the PWM frequency required by most analog servos is 50Hz, which is a period of 20ms. If the frequency is set wrong, for example, to 200Hz, the circuit inside the servo will not be able to correctly analyze the signal, and naturally there will be no response. Remember to initialize the PWM first, and then give a pulse to return the servo to the neutral position (such as 1.5ms high level time) to see if the servo moves slightly.
If you want the servo to rotate smoothly, the code logic is actually not complicated. The core is to continuously change the duration of the high level in the PWM signal, which is the pulse width. Generally, the control pulse width of the servo ranges from 0.5ms to 2.5ms, corresponding to 0 degrees to 180 degrees. When we write code, we can first use a simple for loop to slowly increase the pulse width from 0.5ms to 2.5ms, delaying each step for a short period of time (such as 15ms), so that the servo will smoothly turn from one end to the other. The key is to control the change amount and delay time of each step. If the change is too large, the servo will jump one after another; if the delay is too short, the servo will spin up and overshoot easily. We recommend writing a basic function first, inputting the angle, automatically calculating the corresponding pulse width, and then outputting it to the servo.
After the servo is turned to the designated position, it always differs by a few degrees, which is quite annoying. The position is inaccurate. On the one hand, it is a mechanical error, such as the steering wheel is not fixed properly, or the connecting rod has a false position; on the other hand, the pulse width range and actual angle on the software are not calibrated. The corresponding relationship between pulse width and angle of each servo is slightly different, and the data manual cannot be copied completely. The solution is simple, do a calibration procedure. First write a code to let the servo go to the position you think is 0 degrees, then use a ruler or protractor to measure the actual angle, and record the pulse width value at this time. Then use the same method to measure the pulse width corresponding to 180 degrees. Use these two measured values as the upper and lower limits of your program, so that the control accuracy can be improved a lot. Coupled with the closed-loop control algorithm, the effect will be even better.
What's the weirdest problem you've ever encountered when debugging a servo? Is the drive burned or the program cannot be downloaded? Welcome to share your "rollover" experience in the comment area, or forward the article to a friend who is also tortured by the steering gear, and exchange experiences together!
Update Time：2026-03-10
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